Compositions for safety heating elements



Sept. 20, 1960 w. MAXWELL COMPOSITIONS FOR SAFETY HEATING ELEMENTS FiledMay 2. 1958 QINVENTOR wz'zzz'a m Maxw z ATTORNEYS United States PatentCOMPOSITIONS FOR SAFETY HEATING ELEMENTS William Maxwell, Stevenston,Scotland, assignor to Imperial Chemical Industries Limited, London,England, a corporation of Great Britain Filed May 2, 1958, Ser. No.732,662 Claims priority, application Great Britain Jan. 14, 1953 9Claims. (Cl. 52-7) The present invention relates to heating devicesparticularly suitable for use in blasting devices of the type comprisinga pressure resisting container enclosing a blasting charge for use industy or fiery mines and of the kind capable of undergoingself-sustained flameless gas producing thermal decomposition whenlocally heated, wherein the container is of tubular metal constructionclosed or fitted with a gas-tight closure at one end and at the otherend fitted with a venting cap separated from the container by anexpendable bursting disc adapted to yield at a predetermined pressureand wherein the container is fitted with electrical contacts to enable aheating device to be actuated. More particularly, my invention relatesto a safety heating device for initiating thermal decomposition of anon-detonating safety blasting charge wherein an electric initiatingelement and a heating composition are enclosed in a container, saidheating composition comprising guanidine nitrate, 2545% by Weight of apersulphate compound selected from the group consisting of sodiumpersulphate, potassium persulphate, and ammonium persulphate, and notmore than 10% by weight cuprous chloride, and wherein the container isadapted to release the gas formed within it on initiation of thegas-generating reaction in said heating composition.

This application is a continuation-in-part of United States applicationSerial No. 614,932, now abandoned, which is a continuation-impart ofSerial No. 397,308, now abandoned.

In a charged blasting device of this nature the blasting effect isproduced by the discharge of the gases into the borehole through portsin the venting cap when the pressure within the container has built upsufficiently to cause the bursting disc to yield and a passage has beenopened up between the container and the venting cap. The time taken forthe discharge of the gases from the container into the venting cap andthrough the ports into the borehole after the yielding of the burstingdisc is suflicient to result in a comparatively gentle heaving blastingeifect, such as is desirable for such purposes as the production ofIlumpcoal.

In blasting assemblies of this kind the charge commonly used comprisesan equi-molecular mixture of sodium nitrite and ammonium chloridestabilized with an alkali such as magnesium oxide or sodium carbonate inamounts up to about 3% by weight which when locally heated decomposes ina non-detonating manner without flame in self-sustained fashion with theformation of sodium chloride, nitrogen and steam and under the risingpressure conditions experienced in the aforesaid blasting device thisdecomposition once initiated by the local heating device is greatlyaccelerated and almost immediately the gases are discharged withoutflame, with the result that blasting operations with a charge of thisnature in a blasting device of the aforesaid kind are especially wellsuited for coal-mining in fiery or dusty 111 1168.

In normal practice the decompositionof the charge is initiated by usinga small electric blackpowder fuse as the heating device. This practicehas been possible because although a blackpowder fuse produces flame,the time taken for the decomposition of the stabilized mixture of sodiumnitrite and ammonium chloride to build up a pressure suflicient to causethe bursting disc to yield is long enough for the fragments of theelectric powderfuse to have burned out before the bursting disc yields.Although this type of blasting device using an electric blackpowder fuseas the heating'device is widely used in fiery and dusty mines the natureof the heating device makes it necessary for loading to be carried outabove ground. This causes some inconvenience, for example, considerabletime is lost in taking the tubular containers above ground forrecharging after every 'shot. The use of an electric blackpowder fuse asa heating device for blasting assemblies of the aforesaid nature alsosuffers from various other disadvantages.

It has now been found that the above noted disadvantages can be overcomeby the use of a new heating composition together with an electricinitiating element which, in combination, can be used, for example, inplace 'of a blackpowder fuse to initiate the reaction of compositionscapable of generating sufiicient gas to sustain such reaction. Theability of this new heating composition to be initiated by an electricinitiating element is a significant advantage and is achieved only byutilizing the heating composition disclosed including the specificproportion ranges set forth.

The heating composition contemplated for my novel safety heating devicecomprises guanidine nitrate, 25-45 by weight of a persulphate selectedfrom the group consisting of sodium persulphate, potassium persulphate,and ammonium persulphate, and not more than 10% by weight cuprouschloride. It is preferred to add up to 1% by weight of petroleum jellyto this composition although not mandatory. Petroleum jelly is used inthe composition as an anti-segregation agent If desired, the heatingcomposition of the invention may likewise contain up to about 1% byweight of an oxygen-negative organic fuel other than petroleum jelly,as, for example, castor oil or linseed oil.

It should be stressed that the novel advantages of the safety heatingdevice disclosed and the heating composition used therewith aredependent upon the make-up of the composition and the proportions of thevarious ingredients used. Thus, by my novel invention I have realized aheating composition as understood in the blasting art and particularlysuitable for use to initiate the reaction of a blasting charge. This isachieved more easily and with safety from detonation of inflammable gasmixtures.

With the above in mind, the principal object of this invention is toprovide a safety heating device for initiating thermal decomposition ofa non-detonating safety blasting charge wherein an electric initiatingelement and a heating composition are enclosed in a container, saidheating composition comprising guanidine nitrate, 25-45 by weight of apersulpharte compound selected from the group consisting of sodiumpersulphate, potassium persulphate, and ammonium persulphate, and notmore than 10% by weight cuprous chloride, and wherein the container isadapted to release the gas formed within it on initiation of thegas-generating reaction in said heating composition.

Another object of this invention is to provide a safety heating deviceas noted heretofore wherein the electric initiating element is a lowtension electric fusehead and the cuprous chloride is included in theheating composition in amount of 610% by weight.

An additional object of this invention is to provide a safety heatingdevice as noted heretofore wherein said electric initiating element isin the form of a wire of high electrical resistance adapted to be heatedby an electric current either alone or in conjunction with a smallamount of deflagrating composition and wherein the cuprous chloride ofthe heating composition is in amount of not more than 6% by weight.

Still another object of this invention is to provide a heatingcomposition for use in a safety heating device comprising 45-66% byweight guanidine nitrate, 27-45% by weight of a persulphate compoundselected from the group consisting of sodium persulphate and potassiumpersulphate, and not more than 10% by weight cuprous chloride.

An additional object of this invention is to provide a heatingcomposition for use in a safety heating device comprising 20-70% byweight guanidine nitrate, 25-45% by weight ammonium persulphate, 05-10%by weight cuprous chloride, and not more than 35% by weight of a nitrateselected from the group consisting of am- 'monium nitrate, sodiumnitrate, and potassium nitrate, the total amount of the nitratecompounds being from 55 to 75% by weight.

A further object of this invention is to provide a heating compositionset forth heretofore and including not more than 1% by weight ofpetroleum jelly.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter. It should be understood, however, that the detaileddescription and specific examples, while indicating the preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art, fromthis detailed description.

Reference is made to the accompanying drawings wherein the samereference numbers refer to like parts.

Figure 1 illustrates a safety heating device including one embodiment ofthe invention, and showing the use of a low tension electric fusehead,and

Figure 2 illustrates a safety heating device including anotherembodiment of the invention, and showing the use of a wire of highelectric resistance adapted to .be heated by an electric current inconjunction with a small amount of deflagrating composition.

According to the present invention a safety heating device forinitiating thermal decomposition of a nondetonating safety blastingcharge of the kind wherein an electric initiating element and a heatingcomposition are enclosed in a container is characterized in that theheating composition comprises guanidine nitrate, 25-45% by weight of apersulphate selected from the group consisting of sodium persulphate,potassium persulphate, and ammonium persulphate, and not greater than byWeight cuprous chloride. As noted heretofore, up to 1% by weightpetroleum jelly can be used.

The electric initiating element may be in the form of a wire adapted tobe heated by electric current either alone or in conjunction with asmall amount of a deflagrating composition, for example, in the form ofan electric fusehead. A low tension electric fusehead can sometimes beused, as will be noted hereinafter, depending upon the exact make-up ofthe heating composition and such low tension electric fusehead enablesinitiation of the blasting charge to be eifected using an electricsupply system which would not be adequate for initiation solely by aheated wire.

In connection with the foregoing, the quantity of cuprous chloride inthe heating composition can be up to 6% by weight, if the electricinitiating element is in the 'form of a wire of high electric resistancewith or without deflagrating composition. Only if a low tension electricfusehead is used have "I found it normally necessary to include cuprouschloride in an amount of more than 6% and up to 10% by Weight. Bothmodifications of the invention are contemplated by me. However, thelatter modification is preferred when the safety heating device is to befired in gassy mines. Under such circumstances, a low tension electricfusehead is preferred because initiation thereof can be effected by anelectric supply system of the kind approved for firing in gassy mines,which gives a current of only short duration. Of course, such a currentwould be inadequate to heat a wire of high electric resistance to thetemperature required to effect initiation of the aforesaid heatingcompositions.

It can be appreciated that a reduction of the quantity of cuprouschloride in the heating composition is advantageous in order to enhancethe heating characteristics thereof. Accordingly, where it ispermissible to use a high electrical resistance type of initiatingelement, as for example, in other than gaseous atmospheres, thismodification would be preferred.

It should be noted that potassium persulphate, sodium persulphate, orammonium persulphate, can be used in the heating composition and displaysimilar consistently satisfactory results. The ultimate choice primarilydepends upon the availability of the respective compounds. The additionof the persulphate compound gives a heating composition that is cooler,more sensitive and, therefore, more easily initiated. The end result isa heating composition which is particularly adaptable to use withblasting charges of the type described, which is safe for use inmixtures of inflammable gases, and which is nonexplosive.

A preferred heating composition using potassium persulphate, petroleumjelly and a low tension electric fusehead comprises 60% by weightguanidine nitrate, 31.5% by weight potassium persulphate, 8% by weightcuprous chloride and 0.5% by weight petroleum jelly. It is noted thatthe percentage of cuprous chloride, of necessity, 18 between 6 and 10%in view of the use of a low tension electric fusehead in the safetyheating device.

A preferred composition using potassium persulphate, petroleum jelly anda wire of high electrical resistance, alone or in conjunction with asmall amount of deflagrating composition comprises 62% by weightguanidine nitrate, 34% by weight potassium persulphate, 3% by weightcuprous chloride and 1% by weight petroleum jelly. The use of highresistance wire as the electric initiating element permits decrease ofthe amount of cuprous chloride to under 6%.

A preferred composition using sodium persulphate, petroleum jelly, and ahigh electrical resistance wire comprises 62% by weight guanidinenitrate, 34% by weight sodium persulphate, 3% by weight cuprous chlorideand 1% by Weight petroleum jelly. As previously set forth, in all of thepreferred heating compositions, up to 1% by weight of an oxygen-negativeorganic fuel other than petroleum jelly, such as, for example, castoroil or linseed oil, can be used. Such additives enhance the .stabilityof the heating composition over substantial periods of time, and,accordingly, can be utilized depending upon the specific circumstancesunder which the safety heating device is being used.

The use of ammonium persulphate can also contemplate the inclusion of upto 35 by Weight ammonium, sodium, or potassium nitrate in the heatingcomposition. In this event, the amount of guanidine nitrate can 'be from20% to 70% by weight with the total amount of the nitrate compoundsbeing from 55% to 70% by weight.

In the absence of these other nitrate compounds, the guanidine nitrateis present in the heating composition in amounts of from 45-66% byweight.

It should be stressed that the foregoing discussion regarding thenecessity for more than 6% cuprous chloride when using .a low tensionelectric fusehead is not applicable in the case where other nitratecompounds are added to the heating composition.

A preferred composition using ammonium persulphate, and an additionalnitrate compound, with a low tension electric fusehead comprises 27.0%by weight guanidine nitrate, 40% by weight ammonium persulphate, 2.5 byweight cuprous chloride, and 30.5% sodium nitrate.

It should be emphasized that the heating compositions of the inventiondo not cause ignition of a methane/air mixture containing 9% by volumeof methane when their decomposition is initiated therein. Thus, heatingdevices comprising a charge of these compositions are eminently suitablefor underground loading in blasting devices of the aforesaid type.

The container is preferably made of any convenient non-deflagrating,non-smoulderable material such as for example sheet metal, certainsynthetic resins such as polychloracrylates and fireproofed cardboardbut may also be made of combustible materials provided that thecombustion thereof cannot be initiated by the heating composi tion. Thecontainer may also have a lightly sealed portion adapted to be unsealedby a slight rise in pressure which in itself would not be suflicient torupture the bursting disc of the blasting device or assembly. In apreferred form of the heating device of the invention the containerconsists of a fireproofed cardboard cylinder sealed at one end with awooden plug through which pass two wires leading to a low tensionelectric fusehead and sealed at the other end by a cork which blows outon the generation of slight pressure after initiation.

The safety heating devices of the invention may be used in blastingassemblies of the aforesaid kind in which the main charge comprises anycomposition capable of flameless exothermic gas-producing reaction whenlocally heated, such as are commonly used, but are more ad vantageousfor use with main charge compositions which require a super-atmosphericpressure for their reaction to be initiated. Suitable main chargesinclude ammonium chloride-sodium nitrite mixtures, ammonium nitratecompositions as for example, compositions based on ammonium nitrate andmagnesium nitrate hexahydrate or aluminum nitrate nonahydrate andcompositions based on ammonium nitrate and calcium formate.

The amount of the compositions of the invention used in safety heatingdevices for blasting devices or assemblies of the aforesaid kind mayvary from 1 gram upwards but is preferably from 5-120 grams. tweeninitiation and bursting of the disc of the blasting device or assemblywill, of course, vary according to the amount used. Thus, in a blastingassembly fitted with a mild steel bursting disc inch thick andcontaining a main charge consisting of 380 grams of an equi-rnolecularmixture of ammonium chloride and sodium nitrite and 1.5% by weightmagnesium oxide with a heating device containing a heating chargeconsisting of 60.0% by weight guanidine nitrate, 31.5% by weightpotassium persulphate, 8.0% by weight cuprous chloride and 0.5% byweight petroleum jelly and an electric initiating element consisting ofa low tension electric fusehead for a heating charge weighing 1, 5, 10,20, and 40 grams, the time lag is 32, 10, 5, 2, and 1 secondrespectively. The weight of heating composition used is preferably notless than 5 grams since it is considered undesirable to have a time laggreater than seconds.

In a blasting assembly fitted with a mild steel bursting disc inch thickand using a main charge constisting of 380 grams of equi-molecularmixture of ammonium chloride and sodium nitrite and 1.5% by weight magnesium oxide with a heating charge comprising 62% by Weight guanidinenitrate, 34% by weight sodium persulphate, 3% by weight cuprous chlorideand 1% by weight petroleum jelly, and an electric initiating elementconsisting of a high electric resistance wire, bursting of the discoccurred 28, 12, 6, 2, and 1 second after initiation when the weight ofheating charge was 1, 5, 10, 20, 40, and 120 grams, respectively.

In a blasting assembly fitted with a mild steel bursting disc inch thickand using a main charge consisting of 380 grams of an equi-molecularmixture of ammonium The time lag be- 6 chloride and sodium nitrite and1.5 by weight magnesium oxide with a heater charge comprising 35% byWeight ammonium persulphate, 60.5% by weight guanidine nitrate, 1% byweight potassium nitrate, 2.5% by weight cuprous chloride, 0.5% byweight castor oil and 0.5 by weight china clay, bursting of the discoccurred 35, 30, 15, 9, 3 and 2 seconds after initiation when the weightof the heater charge was 1, 5, 10, 20, 40, and 120 grams, respectively.i The safety heating elements of the invention may also be used fornon-detonating blasting charges of the kind capable of undergoingself-sustained flameless gasproducing thermal decomposition which areused for blasting in boreholes in other devices than of the kinddescribed hereinbefore.

My invention is specifically illustrated by the attached drawings inwhich Figure 1 shows a blasting device of the aforementioned kind inwhich the heating composition 9 is initiated by a low tension electricfusehead 8 and is contained in a paper container, the whole beingcontained within the main charge which is itself prepackaged in a waxedpaper wrapper. Figure 2 illustrates a similar blasting device in whichthe main charge is packed loosely around the heating composition whichis contained in a fireproofed cardboard cylinder and which is positionedby means of the wooden plug 12 which seals one end thereof. A highelectrical resistance wire 19 with deflagrat ing composition thereoncomprises the electric initiating element. With specific reference toFigure 1, a pressure resisting .steel container 1 is of 680 cc. capacityof 1% inch internal diameter and is provided with a mild steel disc 2 ofinch thickness adapted to burst at 12 tons per square inch, a firinghead 3 and a discharge head 4, both of which are of high tensile steel.The pulverulent composition 5 consists of a charge of 170 grams of amixture of 49.2% by weight magnesium nitrate hexahydrate, 38.8% byweight ammonium nitrate, and 12% by weight woodflour enclosed in a waxedpaper wrapper 6 Weighing 20 grams and of inch external diameter. Theloading densisty throughout the tube is 0.25. The electrically actuableheating device embedded in the composition 5 consists of a papercontainer 7 weighing 2 grams and containing a low tension electricfusehead 8 and a 20 gram charge 9 of a heating composition consisting ofby weight guanidine nitrate, 31.5 by weight potassium persulphate,- 8%by weight cuprous chloride and 0.5% by weight petroleum jelly. It can beappreciated that, in Figure 1, element 14 is a cork plug for sealing thecontainer 6, element 15 is a wooden plug for positioning the electricterminal of the leading wires, and element 16 is an insulant to insulateone of the electrodes from the main body of the firing head. Theaforementioned low tension electric fusehead 8 consists of a pole-piecestructure comprising two metal foils separated by an insulant and havingone end of each connected by a resistance bridge wire which has beencoated with a composition comprising lead mon0- nitro-resorcinate andpotassium chlorate in a nitrocellulose dope and finally given a numberof coats of nitrocellulose to render it waterproof.

Turning to Figure 2, the pressure resisting steel container 1 contains320 grams of loose charge 10 consisting of an equi-molecular mixture ofsodium nitrite and ammonium chloride stabilized with 3% of magnesiumoxide.

The electrically actuable heating device comprises a fireproofedcardboard cylinder 11 which weighs 4 grams and which is sealed at oneend by a wooden plug 12 through which pass the wires leading to a wire19 of a high electrical resistance adapted to be heated by an electriccurrent in conjunction with a small amount of deflagrating composition,and which is sealed at the other. end by a cork 13 which blows out onthe generation of a slight pressure after initiation of the 2.0 grams ofheating composition charge 9. Said heating compositioncomprises 62% byWeight guanidine nitrate, 34% by Weight potassium persulphate, 3% byweight cuprous chloride and 1% by weight petroleum jelly.

Other modifications of the invention are more specifically illustratedby the following examples.

Example 1 A blasting device of the kind described and having a mildsteel bursting disc of thickness A inch is charged with a main chargeconsisting of 140 grams of a mixture of 49.0% by Weight ammoniumnitrate, 34.0% by weight magnesium nitrate hexahydrate and 17.0% byweight woodflour and with a heating device comprising 40 grams of amixture of 64% by weight guanidine nitrate, 33.0% potassium persulphate,2.5% by weight cuprous chloride and 0.5% by weight petroleum jellyenclosed in a fireproofed cardboard container with an electric heatingelement as illustrated in Figure 2. The time lag between initiation andbursting of the disc is seconds.

Example 2 The procedure is as in Example 1 except that the compositionin the heating device consists of a mixture of 65.0% by weight guanidinenitrate, 34.5% by weight potassium persulphate and 0.5% by weightpetroleum jelly. The time lag is 35 seconds.

Example 3 The procedure is as in Example 1 except that the compositionin the blasting device consists of a mixture of 62.0% by Weightguanidine nitrate, 31.5% by weight potassium persulphate, 6.0% by weightcuprous chloride and 0.5% by weight castor oil. The time lag is 3seconds.

Example 4 The procedure is as in Example 1 except that the compositionin the heating device consists of a mixture of 64.0% by weight guanidinenitrate, 34.0% by weight potassium persulphate, 1.5% by weight cuprouschloride and 0.5% by weight petroleum jelly. The time lag is seconds.

Example 5 The procedure is as in Example 2 except that the main chargeconsists of a mixture of 63.0% by weight ammonium nitrate, 34.0% byweight calcium formate and 3.0% by Weight woodfiour. The time lag is 5seconds.

Example 6 The procedure is as in Example 5 except that the compositionin the heating device is that used in Example 2. The time lag is 35seconds.

Example 7 A blasting device of the kind described and having a mildsteel bursting disc of thickness inch is charged with a main chargeconsisting of 140 grams of a mixture of 49.0% by weight ammoniumnitrate, 34.0% by weight magnesium nitrate hexahydrate and 17.0% byweight woodflour and with a heating device comprising 40 grams of amixture of 61.0% by Weight guanidine nitrate, 32.5% sodium persulphate,6.0% by weight cuprous chloride and 0.5% by weight castor oil enclosedin a fireproofed cardboard container with an electric heating element asillustrated in Figure 2. The time lag between initiation and bursting ofthe disc is 3 seconds.

Example 8 The procedure is as in Example 7 except that the compositionin the heating device consists of a mixture of 62.0% by weight guanidinenitrate and 34.0% by weight sodium ,persulphate, 3.0% by weight cuprouschloride and 1.0% .by weight castor oil. The time lag is 7 seconds. i l

8 Example 9 The procedure is as in Example 7 except that the compositionin the heating device consists of a mixture of 63.0% by weight guanidinenitrate, 34.5% by weight sodium persulphate, 2.0% by weight cuprouschloride and 0.5% by weight castor oil. The time lag is 10 seconds.

Example 10 The procedure is as in Example 7 except that the compositionin the heating device consists of a mixture of 64.5% by weight guanidinenitrate, 34.0% by weight sodium persulphate, 1.0% by weight cuprouschloride and 0.5% by weight castor oil. The time lag is 13 seconds.

Example 11 The procedure is the same as in Example 7 except that thecomposition in the heating device consists of a mixture of 65.0% byweight guanidine nitrate, 34.0% by weight sodium persulphate and 0.5% byweight castor oil. The time lag is 21 seconds.

Example 12 The procedure is as in Example '7 except that the compositionin the heating device consists of a mixture of 60.0% by weight guanidinenitrate, 31.5 by weight sodium persulphate, 8. 0% by Weight cuprouschloride and 0.5% by weight petroleum jelly and that the electricinitiating element is a low tension electric fusehead as illustrated inFigure 1. The time lag is 4 seconds.

Example 13 The procedure is as in Example 7 except that the compositionin the heating device consists of a mixture of 59.0% by weight guanidinenitrate, 30.5% by weight sodium persulphate, 10.0% by Weight cuprouschloride and 0.5% by weight petroleum jelly and that the electricinitiating element is a low tension electric fusehead as illustrated inFigure 1. The time lag is 4 seconds.

Example 14 A blasting device of the kind described and having a mildsteel bursting disc of thickness & inch is charged with a main chargeconsisting of 320 grams of a loose charge of an equi-molecular mixtureof sodium nitrite and ammonium chloride stabilized with 3% of magnesiumoxide and with a heating device comprising 20 grams of a mixture of30.5% by Weight sodium nitrate, 40.0% by weight ammonium persulphate,27.0% by weight guanidine nitrate, and 2.5% by weight cuprous chlorideenclosed in a fireproofed cardboard container with a low tensionelectric fusehead as illustrated in Figure 1. The time lag betweeninitiation and bursting of the disc is about 5 seconds.

The following comparative data are set forth illustrating the advantagesof the safety heating device and 'heating compositions utilizedtherewith of the present 'invention, over means previously utilized inthe art with particular emphasis on the blackpowder fuse devicespresently in use.

A number of composite charges were made up in fireproofed papercontainers of length 22 inch and 1%; inches in diameter. The main chargein each case consisted of grams of a composition consisting of 49% byweight ammonium nitrate, 34% by weight magnesium nitrate hexahydrate and17% by weight woodflour. The heating elements used consisted of a 40.gram charge of a composition consisting of 60.0% by weight guanidinenitrate, 31.5% by weight potassium persulphate, 8.0% by weight cuprouschloride and 0.5% by weight mineral jelly, Composition A, or 61.5% byWeight guanidine nitrate, 35.0% by weight ammonium persulphate, 2.5% byweight cuprous chloride, 0.5% by weight china clay and 0.5 by weightcastor oil, Composition B, inoonjunction with an electric initiator ofthe kind described in United States Patent No. 2,127,603 in some caseswhile in others the heating element consisted of an electric blackpowderfuse of varying weight. These charges are initiated while being freelysuspended in an atmosphere consisting of 9% by volume of methane in airin order to determine whether accidental initiation of such a charge ina gassy mine could cause ignition of the inflammable gas mixturespresent. The results obtained are given in the table below. It should,of course, be noted that in this test the reaction of the main chargewas not initiated because of the initiation of the heating elementtaking place at atmospheric pressure.

Heating Element Result The novel principles of this invention arebroader than the specific embodiments recited above and rather thanunduly extend this disclosure by attempting to list all the numerousmodifications which have been conceived and reduced to practice duringthe course of this development, these novel features are covered in thefollowing claims.

I claim:

1. A heating composition for use in a safety heating device consistingessentially of guanidine nitrate, 25-45% by weight of a persulphatecompound selected from the group consisting of sodium persulphate,potassium persulphate, and ammonium persulphate, and not more than byWeight cuprous chloride.

2. A heating composition as claimed in claim 1 including up to 1% byweight petroleum jelly.

3. A heating composition as claimed in claim 2 including up to about 1%by weight of an oxygen-negative organic fuel selected from the groupconsisting of castor oil and linseed oil.

4. A heating composition as claimed in claim 1 wherein said guanidinenitrate is in amount of from 45-66% by weight.

5. A heating composition as claimed in claim 1 wherein said guanidinenitrate is in amount of from 20-70% by weight, said persulphate compoundis ammonium persulphate, and wherein said heating composition includesnot more than 35% by weight of a nitrate selected from the groupconsisting of ammonium nitrate, sodium nitrate, and potassium nitrate,the total amount of the nitrate compounds being from -70% by weight.

6. A heating composition as claimed in claim 1 wherein said guanidinenitrate is in amount of by weight, said persulphate is potassiumpersulphate in amount of 31.5% by weight, said cuprous chloride is inamount of 8% by weight and including 0.5% by weight petroleum jel y.

7. A heating composition as claimed in claim 1 wherein said guanidinenitrate is in amount of 62% by weight, said persulphate is potassiumpersulphate in amount of 34% by weight, said cuprous chloride is inamount of 3% by weight and including 1.0% by weight petroleum jelly.

8. A heating composition as claimed in claim 1 wherein said guanidinenitrate is in amount of 62% by Weight, said persulphate is sodiumpersulphate in amount of 34% by weight, said cuprous chloride is inamount of 3% by weight and including 1.0% by weight petroleum jelly.

9. A heating composition as claimed in claim 1 wherein said quanidinenitrate is in amount of 27% by weight, said persulphate is ammoniumpersulphate in amount of 40% by weight, s-aid cuprous chloride is inamount of 2.5% by weight and including 30.5% by weight sodium nitrate.

References Cited in the file of this patent UNITED STATES PATENTS1,143,295 McNabb June 15, 1915 1,309,209 McNabb July 18, 1919 1,669,341Low May 8, 1928 2,142,886 Crater Jan. 3, 1939 2,289,007 Gessler July 7,1942 2,563,491 Thomson et al Aug. 7, 1951 2,604,391 Taylor et al July22, 1952

1. A HEATING COMPOSITION FOR USE IN A SAFETY HEATING DEVICE CONSISTINGESSENTIALLY OF GUANIDINE NITRATE, 25-45% BY WEIGHT OF A PERSULPHATECOMPOUND SELECTED FROM THE GROUP CONSISTING OF SODIUM PERSULPHATE,POTASSIUM PERSULPHATE, AND AMMONIUM PERSULPHATE, AND NOT MORE THAN 10%BY WEIGHT CUPROUS CHLORIDE.